ClipGrab 3.6.1, ported from the Getdeb PPA, should be in the test repository soon. It's an easy to use video downloader and converter for various video hosting sites. I've just tested it for Youtube and the difficult Vimeo sites, including Vevo, and it worked fine, and also for mp3 conversion. Various options and features are explained on its home page.

You'll need to also install ffmpeg (preferably the latest from the test repo) if you want to do any of the automatic video conversions. The program will happily download the original video without ffmpeg, though.